3Com S7906E - Switch, Configuration Manual

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Policy routing
You can also use policy routing to route traffic over an MPLS TE tunnel. In this approach, you need to
create a policy that specifies the MPLS TE tunnel interface as the output interface for traffic that
matches certain criteria defined in the referenced ACL.
This policy should be applied to the incoming interface.
For more information about policy routing, refer to the
QoS Configuration
in the
QoS Volume
.
Automatic route advertisement
You can use automatic route advertisement to advertise MPLS TE tunnel interface routes to IGPs,
allowing traffic to be routed down MPLS TE tunnels.
Two approaches are available to automatic route advertisement: IGP shortcut and forwarding
adjacency.
OSPF and IS-IS support both approaches where TE tunnels are considered point-to-point links and TE
tunnel interfaces can be set as outgoing interfaces.
IGP shortcut, also known as autoroute announce, considers a TE tunnel as a logical interface directly
connected to the destination when computing IGP routes on the ingress of the TE tunnel.
IGP shortcut and forwarding adjacency are different in that in the forwarding adjacency approach,
routes with TE tunnel interfaces as outgoing interfaces are advertised to neighboring devices but not in
the IGP shortcut approach. Therefore, TE tunnels are visible to other devices in the forwarding
adjacency approach but not in the IGP shortcut approach.
Figure 1-3
IGP shortcut and forwarding adjacency
Router D
Router A
Router B
Router C
Router E
10
20
10
10
10
20
As shown in Figure 1-3 , a TE tunnel is present between Router D and Router C. With IGP shortcut
enabled, the ingress node Router D can use this tunnel when calculating IGP routes. This tunnel,
however, is invisible to Router A; therefore, Router A cannot use this tunnel to reach Router C. With
forwarding adjacency enabled, Router A can known the presence of the TE tunnel and thus forward
traffic to Router C to Router D though this tunnel.